Combine the sugar and lemon zest in a medium bowl and set aside for 30 minutes.
Prepare a double boiler by placing 1 inch of water in the pan, and placing it on the stove on medium-low heat, until gently simmering. Combine the eggs and egg yolks in the bowl of the double boiler and whisk until well combined. Add the lemon juice and the zest/ sugar combination. Stir over the heat and add the butter, 1 tablespoon at a time.
Cook in the double boiler, stirring constantly, until the lemon curd reaches 170 degrees. A thermometer is necessary, as the texture will not noticeably change.
When the temperature is reached, remove from the heat. and continue to stir as it cools, for at least 5 minutes. The lemon curd will thicken as it cools. If desired, strain through mesh strainer to remove lemon zest.
Pour into half-pint mason jars. Store in refrigerator for up to 5 days, or freeze for up to 2 months. If freezing, leave at least half an inch of space at the top of the jar.
To waterbath can: place in hot but not boiling (180 degree) water in canner, turn up heat until water is boiling, and then process 15 minutes (start timing when water is boiling). Higher elevations will require additional processing time, Will store well at room temperature for 2 months, after which the lemon curd will discolor and turn brown.
Keywords: lemon curd, freezer safe lemon curd, lemon curd from scratch, spring canning